MXS-2402 Document and handle 'check_unions' parameter

Only parameter handling, no actual functionality.

Documentation/Filters/Masking.md

@@ -79,6 +79,14 @@ Please see the configuration parameter
 [check_user_variables](#check_user_variables)
 for how to change the default behaviour.
 
+From MaxScale 2.3.5 onwards, the masking filter will examine unions
+and if the second or subsequent SELECT refer to columns that should
+be masked, the statement will be rejected.
+
+Please see the configuration parameter
+[check_unions](#check_unions)
+for how to change the default behaviour.
+
 ## Limitations
 
 The masking filter can _only_ be used for masking columns of the following
@@ -192,6 +200,20 @@ check_user_variables=false
 
 The default value is `true`.
 
+#### `check_unions`
+
+This optional parameter specifies how the masking filter should
+behave with respect to UNIONs. If true, then a statement like
+```
+SELECT a FROM t1 UNION select b from t2;
+```
+will be rejected if `b` is a column that should be masked.
+```
+check_unions=false
+```
+
+The default value is `true`.
+
 ## Rules
 
 The masking rules are expressed as a JSON object.

server/modules/filter/masking/maskingfilter.cc

@@ -127,6 +127,12 @@ extern "C" MXS_MODULE* MXS_CREATE_MODULE()
                 Config::check_user_variables_default,
                 MXS_MODULE_OPT_NONE,
             },
+            {
+                Config::check_unions_name,
+                MXS_MODULE_PARAM_BOOL,
+                Config::check_unions_default,
+                MXS_MODULE_OPT_NONE,
+            },
             {MXS_END_MODULE_PARAMS}
         }
     };

server/modules/filter/masking/maskingfilterconfig.cc

@@ -28,6 +28,7 @@ const char config_value_always[] = "always";
 
 const char config_name_prevent_function_usage[] = "prevent_function_usage";
 const char config_check_user_variables[] = "check_user_variables";
+const char config_check_unions[] = "check_unions";
 
 const char config_value_true[] = "true";
 }
@@ -88,11 +89,22 @@ const char* MaskingFilterConfig::prevent_function_usage_default = config_value_t
 /*
  * PARAM check_user_variables
  */
+// static
 const char* MaskingFilterConfig::check_user_variables_name = config_check_user_variables;
 
 // static
 const char* MaskingFilterConfig::check_user_variables_default = config_value_true;
 
+/*
+ * PARAM check_unions
+ */
+// static
+const char* MaskingFilterConfig::check_unions_name = config_check_unions;
+
+// static
+const char* MaskingFilterConfig::check_unions_default = config_value_true;
+
+
 /*
  * MaskingFilterConfig
  */
@@ -130,3 +142,9 @@ bool MaskingFilterConfig::get_check_user_variables(const MXS_CONFIG_PARAMETER* p
 {
     return config_get_bool(pParams, check_user_variables_name);
 }
+
+// static
+bool MaskingFilterConfig::get_check_unions(const MXS_CONFIG_PARAMETER* pParams)
+{
+    return config_get_bool(pParams, check_unions_name);
+}

server/modules/filter/masking/maskingfilterconfig.hh

@@ -48,6 +48,9 @@ public:
     static const char* check_user_variables_name;
     static const char* check_user_variables_default;
 
+    static const char* check_unions_name;
+    static const char* check_unions_default;
+
     MaskingFilterConfig(const char* zName, const MXS_CONFIG_PARAMETER* pParams)
         : m_name(zName)
         , m_large_payload(get_large_payload(pParams))
@@ -55,8 +58,10 @@ public:
         , m_warn_type_mismatch(get_warn_type_mismatch(pParams))
         , m_prevent_function_usage(get_prevent_function_usage(pParams))
         , m_check_user_variables(get_check_user_variables(pParams))
+        , m_check_unions(get_check_unions(pParams))
     {
     }
+
     ~MaskingFilterConfig()
     {
     }
@@ -91,6 +96,11 @@ public:
         return m_check_user_variables;
     }
 
+    bool check_unions() const
+    {
+        return m_check_unions;
+    }
+
     void set_large_payload(large_payload_t l)
     {
         m_large_payload = l;
@@ -115,9 +125,14 @@ public:
         m_check_user_variables = b;
     }
 
+    void set_check_unions(bool b)
+    {
+        m_check_unions = b;
+    }
+
     bool is_parsing_needed() const
     {
-        return prevent_function_usage() || check_user_variables();
+        return prevent_function_usage() || check_user_variables() || check_unions();
     }
 
     static large_payload_t      get_large_payload(const MXS_CONFIG_PARAMETER* pParams);
@@ -125,6 +140,7 @@ public:
     static warn_type_mismatch_t get_warn_type_mismatch(const MXS_CONFIG_PARAMETER* pParams);
     static bool                 get_prevent_function_usage(const MXS_CONFIG_PARAMETER* pParams);
     static bool                 get_check_user_variables(const MXS_CONFIG_PARAMETER* pParams);
+    static bool                 get_check_unions(const MXS_CONFIG_PARAMETER* pParams);
 
 private:
     std::string          m_name;
@@ -133,4 +149,5 @@ private:
     warn_type_mismatch_t m_warn_type_mismatch;
     bool                 m_prevent_function_usage;
     bool                 m_check_user_variables;
+    bool                 m_check_unions;
 };